A wide variety of electronic writing systems have been proposed. In general, an electronic writing system allows a user to interface with a computer or other electronic device using a writing instrument (often referred to as a “digital pen” or a “stylus”). The electronic writing system includes means for recording the positions of the writing instrument across a substrate over time. These positions are recorded as strokes or traces. The recorded traces may be stored in the form of a virtual copy of the original movements of the writing instrument or they may be interpreted by the electronic writing system. For example, the recorded traces may be interpreted by a handwriting recognition system, which converts the traces into text input. In some implementations, an electronic writing instrument also is configured to mark a substrate with ink or other marking agent, thereby providing a hard copy of the paths traversed by the electronic instrument at the same time the virtual copies of the paths are recorded.
In one approach, a digital pen has an ink writing tip that includes a light source in a pen body that directs light toward paper over which the writing tip is moved. A camera mounted in the pen body captures images of areas of the paper that are illuminated by the light source. A processor in the pen body determines pen motion based on the captured images. A contact sensor in the pen body senses when the tip is pressed against the paper, with positions being recorded on a nonvolatile memory in the pen body only when the contact sensor indicates that the pen is pressed against the paper. Periodically, key frame images captured by the camera are stored in memory. The memory may be attached to a handwriting recognition device, which correlates the key frames and positions to alpha-numeric characters. The digital pen may be used with ordinary paper, quad-ruled paper, and special bar-coded paper that allows the system to determine absolute pen position.
In another approach, an electronic writing device includes an elongated housing that has a tip configured to contact a surface. The electronic writing device also includes a pressure sensor disposed within the housing. The pressure sensor is coupled to the tip and is configured to detect when the tip contacts the surface. The electronic writing device further includes first and second acceleration sensors disposed within the housing and adjacent the tip of the marking device. The first and second acceleration sensors are configured to sense acceleration of the tip in first and second directions. Responsive to the sensing of acceleration, the first and second acceleration sensors generate first and second signals indicative of acceleration in first and second directions. The electronic writing device also includes a conversion device, such as an analog-to-digital converter, that converts the first and second signals into at least one computer readable signal that is used to generate data relating to the motion of the housing.